ANGLE MODULATION

DIKSHA PRAKASH

TOPICS COVERED

• Introduction• Concept of Angle Modulation : Basic Definition

– Phase Modulation (PM) Definition– Frequency Modulation (FM) Definition

• Frequency Deviation• Relationship between Phase Modulation (PM)

and Frequency Modulation (FM)• Single Tone Frequency Modulation

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INTRODUCTION

• Frequency or phase of message signal is varied according to the message signal.

• The amplitude is kept constant.

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Concept of Angle Modulation : Basic DefinitionDEFINITION

Total phase angle of the carrier wave is varied according to the instantaneous value of the modulating signal keeping the amplitude constant.

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TYPES OF ANGLE MODULATION

• Depending upon the ways in which we can vary phase angle ‘Ǿ’, the types are:

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APPLICATIONS OF ANGLE MODULATION

• Radio Broadcasting• Two way mobile radio• Microwave communication• TV sound transmission• Cellular radio• Satellite communication

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ADVANTAGES AND DISADVANTAGES

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PHASE MODULATION

Phase angle Ǿ is varied in accordance to baseband or modulating signal.

The mathematical representation of the same can be shown as:

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FREQUENCY MODULATION

• It is a type of angle modulation in which the instantaneous frequency varied linearly in accordance to baseband or modulating signal.

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FREQUENCY MODULATIONNegative Deviation

PositiveDeviation

FIGURE: Illustration of Frequency Deviation

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Frequency Relationship between PM and FM

Expression for PM wave is:

Expression for FM wave is:

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• In PM, the phase angle varies linearly with base band signal x(t).

• In FM, the phase angle varies linearly with the integral of baseband signal x(t).

Thus, FM can be obtained from FM and the converse is also true.

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FM using PM

FM signalAn Integrator

Phase Modulator

Carrier Generator

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PM using FM

A Differentiator

Frequency Modulator

Carrier Generator

PM Signal

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SINGLE TONE FREQUENCY MODULATION

• General expression for FM wave:

Equation shows non-linear modulation process. Hence to avoid complexity, we use single tone frequency modulation.

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INFERENCES

• Frequency of carrier wave is varied according to x(t).

• Maximum amplitude of the carrier wave is kept constant.

• • This deviation is called ‘Frequency Deviation’• Amount of deviation depends upon

amplitude of x(t)

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• For FM, the modulation index is denoted by:

or,

The modulation index maybe greater than unity.

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MATHEMATICAL EXPRESSION & NUMERICALS

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